Optical system having unlimited depth of focus

ABSTRACT

An optical system for use in a microscope and other optical systems has an unlimited depth of focus. The optical system comprises at least one lens, rotating mechanisms for continuously oscillating the focal length of the lens, and opaque elements for momentarily preventing light to pass through the lens. The rapid (i.e., greater than about 16 images a second) and sequential replacement of images in a plane parallel to and a fixed distance will provide an unlimited depth of focus to elicit in the observer a sense of sharp focus of the entire observed object.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to optical systems and, moreparticularly, to optical systems that have an unlimited depth of focus.

[0003] 2. Description of Related Art

[0004] A well-known problem encountered with all optical systems is thatfor any system there is a relatively finite depth of focus, i.e., afixed range of focus wherein portions of an object or one or moreobjects are in focus at the same time. A greater depth of focus isdesired for presenting to the observer a more complete image of thatwhich is observed. As is well known to those skilled in the art, thedepth of focus of a lens system can be increased by increasing the focallength of the lens system and/or using smaller diameter apertures.

[0005] In the focus of microscopes, such as used for surgery orbiological research, problems arise with using these prior approaches ofincreasing the depth of focus. In microscopes, there is a practicallimit as to the useful length of the lens systems so the focal length islimited. As the magnification increases for a microscope, the depth offocus necessarily decreases, so that with most microscopes the observeris presented with an extremely thin visual image of the observed objectthat is in focus. When the diameter of the aperture is reduced, thisnecessarily limits the amount of light that is presented to theobserver. To increase the brightness of the visual image, higherintensity lights must be directed at the observed object, either inreflected light systems or for transmitted light systems, which cancause actual harm to the observed object, such as living tissue.

[0006] Other methods of increasing the depth of focus of an opticalsystem involve relatively complicated mechanisms to move or rapidlyadjust the focus of the optical system, so that the observer ispresented with a series of in focus images taken along a plurality ofparallel planes passing through the observed object. The trouble withthis arrangement is that the depth of focus remains the same, and onlythe focus is varied manually or by some mechanized means. Some of theseprior optical systems are described in U.S. Pat. Nos. 4,448,498;4,863,252; 5,054,896; 5,321,447; and 5,351,152.

SUMMARY OF THE INVENTION

[0007] The present invention has been contemplated to overcome theforegoing deficiencies and meet the above described needs. Specifically,the present invention comprises at least one lens, rotating mechanismfor continuously oscillating the focal length of the lens in stepwiseincrements, and opaque elements for momentarily preventing light to passthrough the lens. The present invention permits a rapid and sequentialpresentation to the observer of in-focus images in a plane parallel toand at a fixed distance from the lens system to provide an unlimiteddepth of focus that elicits in the observer a sense of sharp focus ofthe entire observed object.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008]FIG. 1 is a semi-diagrammatic elevational view of a preferredembodiment of a lens system of the present invention, with a rotatingcarriage of lens elements.

[0009]FIG. 2 is a plan view of the lens system of FIG. 1.

[0010]FIG. 3 is a semi-diagrammatic elevational view of an alternatepreferred embodiment of a lens system of the present invention, withdual rotating carriages of lens elements.

[0011]FIG. 4 is a plan view of the lens system of FIG. 3.

[0012]FIG. 5 is a cutaway side view of the edge between two adjoininglens elements.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] The present invention is a lens system with an unlimited depth offocus, and is an improvement upon the lens system disclosed in U.S. Pat.No. 5,896,223, which has common inventorship herewith and which isherein incorporated by reference. The lens system of the presentinvention can be used within almost all forms of optical systems, suchas still cameras, movie cameras, television cameras, binoculars,telephoto lenses, cathode ray tubes, image projection systems, andmicroscopes. For the purposes of the present discussion, the presentinvention will be referred to as being part of a microscope, and moreparticularly part of a mono- or bi-ocular microscope as used in surgery.

[0014] One of the major principles of the operation of the presentinvention is the well-known neuro-optical phenomena called “flickerfusion”, whereby the eye is presented with a sequential presentation ofimages to create the illusion of motion. Specifically, the effect ofmotion is achieved by the rapid sequential changing of frames of a moviefilm in a plane that is oriented parallel to and at a fixed distancefrom the object. This effect takes place when the frequency of imagechange is about 16-24 frames per second or greater. The inventors hereofhave adapted this “flicker fusion” principle into a lens system toprovide an unlimited depth of focus for a lens system.

[0015] For the purposes of the present discussion, the term “unlimiteddepth of focus” means that the depth of focus of a preferred embodimentof the lens system of the present invention is greater than the depth offocus of a substantially identical prior lens system with a fixed depthof focus. Care should be taken to note that “unlimited” does not meaninfinite or without end, but it means that it is not normallyconstrained. As will be described in more detail below, one preferredmethod for achieving an unlimited depth of focus is by having at leastone lens and a rotating mechanism for continuously oscillating the focallength of the lens in stepwise increments. This repetitive change infocal length by a specific increments (e.g., distance) and sufficientfrequency (e.g., changes of images per second) will elicit in theobserver a sense of sharp focus of the observed object. In other words,instead of providing the observer with a single very thin plane of focus(as in prior lens systems), the present invention provides the observerwith an in-focus relatively thick stack of planes of focus.

[0016] To ensure clarification of what is meant by the terms“continuously oscillating” and “stepwise increments”, the followingshould be understood. The above wording is not restricted to any actualvertical movement of a lens. All that is required is that the focallength of the lens be oscillated, i.e., from one value Y-min. to anothervalue Y-max., and then back, and in stepwise increments, i.e., value Y1,Y2, . . . These increments can have a stop-start motion or be smooth andcontinuous. So, the “oscillating” can occur by the rotational movementof the lens and/or one or more lens elements.

[0017] Turning now to the drawings, FIGS. 1 and 2 show one preferredembodiment of the present invention wherein an object 10 to be observed,such as all or a portion of an anatomical specimen, is located generallywithin the longitudinal optical axis 12 of a lens system 14 of thepresent invention. An eye 16 of an observer is shown viewing a magnifiedoptical image of the object 10, in line with the longitudinal opticalaxis 12, through a magnifying eye piece or ocular 18, having one or morelens elements. The lens system 14 has an adjustable diaphragm 20, withinthe ocular 18 or adjacent thereto, to adjust the amount of light thatpasses there through. This diaphragm 20 is particularly helpful whenviewing a wet or highly reflective object 10 under high intensity light,such as provided by a light source 22. In addition, the smaller thediaphragm opening, the greater the depth of focus of the lens system, asis well known to those skilled in the art. An intermediate tubular lens24, comprising one or more optical elements, may be included, and whichis spaced from the ocular 18 and lies within the longitudinal opticalaxis 12.

[0018] The embodiment shown in FIGS. 1 and 2 are for a single lenssystem, and an alternate preferred embodiment is shown in FIGS. 3 and 4for a dual lens system, such as used in a surgical microscope. In onepreferred embodiment a circular carriage 26 is rotated, preferablycontinuously and smoothly, about a vertical axle 28 by a gear and/or abelt and motor mechanism 30. The carriage 26 rotates about a verticalaxis that is parallel to the optical axis 12. An outer radius portion ofthe carriage 26 rotates through the optical axis 12 between one or morelens fixed elements 32 and 34. This outer radius portion of the carriage26 includes a ring 36 of a plurality of lens elements 38. Each lenselement 38 has essentially the same (constant) optical characteristicsacross its dimensions, yet each lens element 38 has a different opticalcharacteristic from the immediately adjacent lens element 38. Theoptical characteristics of the lens elements 38 vary by havingdifferences in material, density, color, polarization, types of opticalcoatings, shape, thickness, and/or curvature.

[0019] The ring 36 has the lens elements 38 arranged in a pattern sothat as each lens element 38 is rotated through the optical axis 12 asequence of images is presented to the observer 16. For example, thering 36 in FIG. 2 has 8 individual lens elements 38, and the pattern ofoptical characteristics can vary sequentially, such as elements #1, 2,3, . . . , 7, 8, 1, 2, . . . However, the lens elements 38 can vary in arepeating pattern, such as elements #1, 2, 3, . . . , 7, 8, 7, . . . ,3, 2, 1; or, any other pattern may be used as desired.

[0020] It should be noted that since each lens element 38 hasessentially the same (constant) optical characteristics across itsdimensions, so that as each lens element 38 is rotated through theoptical axis 12, the image presented to the observer 16 will remainessentially the same during that time period, even though the lenselement 38 is continuously moving. To provide the observer with thedesired unlimited depth of focus through the rapid and sequentialreplacement of differing visual images, a series of opaque elements 40are interspersed between the lens elements 38. These opaque elements 40can be any desired shape, size and configuration and made from anydesired material as long as each element 40 prevents the passage oflight there through. One preferred embodiment is for the opaque elementsto be made from opaque styrene plastic to reduce weight in relation tousing a metallic material. It is preferred to have the opaque elements40 be of relatively short in length in comparison to the length of thelens elements 38. This is to allow the maximum amount of light to passthrough to the eye 16 of the observer and to minimize the duration ofany “blanking” caused by an opaque element 40 passing through theoptical axis 12.

[0021] The inventors hereof have found that the opaque elements 40 actas a shutter to momentarily block the image passing to the eye 16 of theobserver when there is a transition from one image to the next. In otherwords, when the trailing edge of a first lens element 38 comes to theoptical axis 12, there should be a blockage of an image until theleading edge of the next lens element 38 passes past the optical axis12. In certain circumstances where the absolute maximum amount of lightis needed to pass to the observer, the use of the opaque elements 40 maynot be desired. The inventors hereof have found that with a relativelyrapid rotation of the carriage 26, such as from about 60 rpm to about150 rpm, the opaque elements 40 can be eliminated and still provide acrisp image transition from one lens element 38 to the adjacent lenselement.

[0022] The inventors have found that the abutting edge between adjacentlens elements 38 are preferably matched and configured to provide anoptically distinct transition. FIG. 5 shows an abutting edge 42 formedbetween a first lens element 44 and an adjacent second lens element 46,which has a different optical characteristic than the first lens element44. This edge 42 is preferably formed by having the respective sideedges of the lens elements 44 and 46 being formed and polished so as tobe parallel to the optical axis 12, and straight as possible throughtheir radial extent. One edge or both edges of the lens elements 44 and46 are preferably polished to be optically transparent. The result isthat as each abutting edge 42 passes through the optical axis 12 thereis a crisp and clear optical break between the optical image presentedby the lens element 44 and then the lens element 46.

[0023] The inventors hereof have found that the lens systems 14 shown inFIGS. 1-5 have at least two advantages over prior systems thatvertically move the lens, especially when used in relatively highmagnification systems. First, is the reduction in vibration caused bythe elimination of the incremental vertical movement of the lenses.Second, is the ability to provide a brighter image to the viewer. Thebrighter image is a result of the absence of a shutter and the lenselements 38 being within the optical axis a majority of the time due totheir relative greater length as compared to the length of the opaqueelements 40. Further, in the alternate preferred embodiment, thebrightest image is obtainable due to the absence of any opaque elements40.

[0024] The inventors hereof have found that the principle of “unlimiteddepth of focus” can be used in any device or system where lenses areused. Yet, conventional lens structures need not be used. The principlecan be adapted for use with lenses formed from one or more crystals,crystal laminates, plastic or ceramic laminates, gels, gasses, andliquids. In addition, actual physical movement of one or more of thelenses need not occur to change the focal length in the mannercontemplated herein.

[0025] As has been described above, with the present invention light ispermitted to pass through the lens system when the lenses, and thereforethe focal length of the lens system, are momentarily fixed and light isprevented from passing through the lens set when the focal length is notmomentarily fixed. The rapid and sequential replacement of differingvisual images presented to an observer in a parallel plane and at afixed distance provide an unlimited, i.e., far greater than previouslyobtainable with a comparable prior lens system, depth of focus to elicitin the observer a sense of sharp focus of the observed object.

[0026] Whereas the present invention has been described in relation tothe drawings attached hereto, it should be understood that other andfurther modifications, apart from those shown or suggested herein, maybe made within the scope and spirit of the present invention.

What is claimed is:
 1. An optical system having unlimited depth offocus, comprising: at least one lens; rotating mechanism forcontinuously oscillating the focal length of the lens in stepwiseincrements; and opaque elements for momentarily preventing light to passthrough the lens.
 2. An optical system having unlimited depth of focus,comprising: at least one lens; rotating mechanism for continuouslyoscillating the focal length of the lens; and opaque elements carried onthe rotating mechanism for preventing light to pass through the lens. 3.An optical system having unlimited depth of focus, comprising: at leastone lens; rotating mechanism for continuously oscillating the focallength of the lens in stepwise increments; and opaque elements carriedon the rotating mechanism for preventing light to pass through the lenswhen the focal length is not momentarily fixed.
 4. An optical systemhaving unlimited depth of focus, comprising: a plurality of lens sets,each comprising at least one optical element, and each having adifferent optical characteristic; rotating mechanism for continuouslyand sequentially moving the lens sets into line with a longitudinaloptical axis of the lens system; and opaque elements for momentarilypreventing light to pass to the viewer when one of the lens sets is notmomentarily fixed in position.
 5. An optical system of claim 4 whereinthe plurality of lens sets are carried upon a carriage that rotatesabout a longitudinal axis parallel to the optical axis.
 6. An opticalsystem having unlimited depth of focus, comprising: a plurality of lenssets, each comprising at least one optical element, and each having adifferent optical characteristic; rotating mechanism for continuouslyand sequentially moving the lens sets into line with a longitudinaloptical axis of the lens system; and opaque elements carried on therotating mechanism for momentarily preventing light to pass to theviewer when one of the lens sets is not momentarily fixed in position.7. An optical system of claim 6 wherein the plurality of lens sets arecarried upon a carriage that rotates about a longitudinal axis parallelto the optical axis.
 8. An optical system having unlimited depth offocus, comprising: a lens set comprising a plurality of optical elementseach having a different optical characteristic; rotating mechanism forcontinuously moving the optical elements into line with a longitudinaloptical axis of the lens system; and opaque elements for preventinglight to pass to the viewer during an image transition.
 9. An opticalsystem of claim 8 wherein the plurality of optical elements are carriedupon a carriage that rotates about a longitudinal axis parallel to theoptical axis.
 10. An optical system having unlimited depth of focus,comprising: at least one lens; and rotating mechanism for continuouslyoscillating the focal length of the lens.
 11. An optical system of claim10 wherein the rotating mechanism continuously oscillates the focallength of the lens in stepwise increments.
 12. An optical system havingunlimited depth of focus, comprising: a first optical element and asecond optical element, each having a different optical characteristic;rotating mechanism for sequentially moving the first and the secondoptical elements into line with a longitudinal optical axis of the lenssystem; and abutting edges of the first optical element and the secondoptical element being configured to form an optically distincttransition.
 13. An optical system of claim 12 wherein the opticalelements are carried upon a carriage that rotates about a longitudinalaxis parallel to the optical axis.